Tales from the front line in the hunt for the perfect SCART television for use with the MAME arcade game emulator.

Wednesday, 19 September 2012

How to customise a SCART TV for use with GroovyUME

(Work-in-progress post! Further info and images coming soon!)

This guide will detail the steps involved in modifying a Blaupunkt IS 70-33 VT television for use with GroovyUME in order to make the most of the world of native 15kHz video emulation using a real CRT display in conjunction with a PC to play arcade and consoles games. This post is intended to retrace the steps involved setting up my Blaupunkt IS 70-33 VTN as detailed here and here.

The completed modification will include externalization of the image control potentiometers and also upgrading the Philips tube found in the Blaupunkt with a newer tube from a Loewe CT 1170 television. Once complete, this TV will feature a formidable combination of an analog chassis and a high-grade, Black Matrix tube.

Loewe and Blaupunkt

Blaupunkt (top) and Loewe (bottom)

Back story:

The Loewe CT 1170 is a fantastic television. The case is made from heavy plastic, the tubes look fantastic and the E3000 chassis provides a particularly sharp and stable image. The only problem is that this digital chassis type is fairly inflexible when it comes to the wide variety of video modes that GroovyUME outputs. For a start, the E3000 seems incapable of displaying more that 224 vertical lines in NTSC mode (e.g. at 60 Hz). This limitation is fine for many popular arcade games (e.g. CPS1/2/3 and Neo Geo) but games that use 240 or 256 vertical lines get cropped. This is a serious downer if you want to play Irem games or Mortal Kombat.

Also, image adjustment on the E3000 is via a Service Menu. There are a lot of options that can be tweaked in order to get the image just right but it's a slow process. If you want to play games with the screen properly filled and with perfect geometry, you'll soon grow tired of getting in and out of the E3000 Service Menu between video modes.

The benefit of using the Grundig CUC 5360 analog chassis (as used in the Blaupunkt featured) is the greater compatibility between video modes and the ability to quickly tweak the image size using analog pots. Adjusting the sizing and position using a knob you can physically grab is many magnitudes faster than navigating an OSD driven Service Menu. The effect is instantaneous and it's a very gratifying feeling to see games fill the screen every time rather than putting up with black borders or missing pixels.

Loewe CT 1170 (chassis type E3000)

Blaupunkt IS 70-33 VT (chassis type FM 310.32)

Preparations the donor tube:

The first step in this operation is to remove the tube from the CT 1170. To do this, we first take the back case off:

Rear

Back panel removed

Before going any further, I like to clean out all the dust and grime out using an air compressor. TVs accumulate layers of dust over the years and it's like to get that out of the way before commencing work. It makes the whole process much more enjoyable...

Next, we're ready to start disconnecting the chassis. There are a few connections to sort out before we start removing the yoke.

Disconnect the left and right speaker cables (coil these up neatly).

Disconnect the degauss cable and roll it up.

Disconnect the dag wire from the tube earthing (this green wire runs from the neckboard).

Remove the neckboard by gently pulling the socket away from the neck.

Disconnect the anode using a discharge tool (CAUTION! This is dangerous!)

Now we're ready to start removing the yoke. The first step is to loosen the neck clamp using an allen key:

Yoke clamp closed

Yoke clamp open

Next, using a sharp cutting knife, we need to carefully slice through the silicon glue that holds each of the yoke feet in place. Make sure that all movements are controlled so as not to accidentally damage the yoke windings:

Slice the silicon under each foot

Yoke cut free from the tube

With the neck clamp loosened and the silicon blobs severed, the yoke will now slide off the neck. Be very careful not to damage the neck during this process! If the shaft of the neck cracks, the tube will be ruined! However, there shouldn't be any problem if care is taken:

Yoke removed from the neck

Now the entire chassis can be removed from the plastic housing. Undo the screws that fasten the main PCB board into the case. Then, disconnect the cables that connect the chassis to the front panel PCB at the front of the TV case (this PCB holds the function buttons and power switch). Once these are disconnected, the chassis will slide right out:

E3000 chassis removed

TV with chassis removed

Now, the tube can be removed. To do this, lay the TV face down first:

Loewe CT 1170 face down

Then, undo each of the four screws that hold the tube to the TV casing using a 1/8" socket:

Undo each of the 4 screws

Once the screws are removed, the tube can be lifted out. With an A66EAK Philips tube, lifting the tube without the help of another person is awkward but it can be done if care is taken:

Tube removed

Once the tube is out, remove the degauss cable, ground strap and plastic braces. Then, the back of the tube can be dusted with a cloth and the screen can polished. Once completed, the donor tube is ready for action!

Cables removed, tube cleaned

Philips A66EAK071X11 tube

Preparing the recipient:

Next, our attention turns to the Blaupunkt. Remove the back cover and clean thoroughly with an air gun:

Blaupunkt (back cover)

Blaupunkt (back cover removed)

Dusty chassis

Take note of how all the cables are folded in place. It's best to take photos for future reference:

Loosen the two screws holding the chassis in position and slowly slide it out:

Blaupunkt chassis removed from case

Now, lay the TV face down and remove the tube, following the sames steps as the Loewe:

Tubes before swapping the degauss coil

Put the two tubes beside each other and exchange all the components from one to the other:

Remove the degauss cable (be careful to maintain the shape though).

Remove the plastic straps (white coloured).

Remove the ground strap (usually held in plastic with an elastic band and spring).

Transfer the black plastic clips from the old tube to the next (match up the same positions).

Place the ground strap onto the new tube.

Place the middle straps onto the new tube.

Insert the degauss coil back into the correct position (using the plastic clips).

Tubes after swapping the degauss coil and earth strap

The donor tube is now ready for use with the Blaupunkt chassis!

Drilling holes for the pots:

While the tube is out of the TV case, it's time to drill holes for the 6 potentiometers. To aid in this, cut out a two template to align the holes:

Drilling templates

Holes marked out

Paper template aligns with plastic struts

Next, say a little prayer and drill the holes! For the cleanest results, use a brad point drill bit. For the Vishay pots used in this project, a 10mm drill bit is required. In this instance, the holes I drilled turned out very clean indeed:

Holes drilled with template in position

Template removed

Removing the trimpots:

Next, the original trimpots need to be removed from the chassis PCB. The following chart shows which pots are will be replaced:

Potentiometer values and Vishay part numbers

These can be desoldered using some solder wick:

PCB with trimpots removed (bottom view)

PCB with trimpots removed (top view)

Original trimpots removed from the PCB

A nice touch is to clean the surrounding area with some circuit board cleaner and a soft bristle toothbrush. This will remove any flux and grime making the holes cleaner and nicer to work with.

Heat shrink one of the 15mm over the point where the insulation was removed (allow 5 mm overlap).

Cable preparation

Prepare the pots:

Tin the 3 solder lugs on the pots.

Place 3 lengths of heat shrink over each conductor.

Solder the conductors in place.

Apply the heat shrink to each lug.

Label the outer cable with a fine marker (resistor values and control name).

Patch cable labels

Pot preparation

Install the pots:

Insert each cable and pot into the correct hole. From left-to-right, the order I chose is as follows:

Vertical Size (V-Size)

Vertical Position (V-Pos)

Horizontal Size (H-Size)

Horizontal Position (H-Pos)

Pincushion (Pin)

Trapezium (Trap)

Once the patch cables have been put into position, slice the nut over the cable end and temporarily fasten the pots in place. Turn all the pots to their minmum value (anti-clockwise). Carefully adjust the rotation of each shaft (from the rear) so that each white dot lines up neatly along the front panel:

Pots mounted

Once satisfied, tighten the nuts properly and apply a blob of hot glue to the back of each pot (and nut) to make sure it remains in place.

Solder the patch cables:

Now it's time to attach the patch cables to the main PCB. Match the labels marked on the cable ends with the numbers on the top of the PCB. Lay the chassis on its side to do this.

Re-assemble the TV:

The operation is now nearing completion! The final step is to re-assemble the TV. The hardest part is carefully placing the tube back into the case without accidentally dropping it on the chassis (which is now attached via the patch cables).

Lay the TV flat on the floor (screen down) and move the patch cables and chassis safely out of the way.

Replace the anode carefully. Make sure the clips are firmly gripping the anode hole.

Attach the chassis ground wire (white) and neckboard ground (black) to the ground strap on the tube.

Double check that all cables have been re-attached and that they are neat and tidy. Then, screw the chassis back into position.

Now, it's time to fit the yoke by sliding it back onto the neck. Gently push it in close to the tube and level it with the screen as best you can. Tighten the neck clamp lightly, leaving it loose enough to allow rotation. The yoke will need to be positioned more precisely by checking with the actual image on the screen once the TV is powered up.

Now, triple check everything! Go back through the list and make sure everything is securely plugged into the correct place and that no cables are unaccounted for. Serious damage can result if the TV is powered on without a key cable attached!

Once all the connections have been thoroughly checked, the TV can be switched on! With no aerial plugged in, you should see snow. Adjust the picture roughly so that the image fits:

Rough picture sizing before the yoke is aligned

Now, plug in a computer using a VGA to SCART cable!

Align the yoke:

Bring up a test grid at 320 x 240 in Arcade_OSD.

Adjust the vertical size and position controls so that the top and bottom borders come to the edge of the tube mask.

Gently rotate the yoke left or right to straighten the top and bottom borders on screen with the tube mask.

You may have to compromise a little between having the top and bottom perfect.

Once satisfied, gently tighten the neck clamp until the yoke will no longer rotate.

Lay the TV flat and apply some hot glue to the yoke feet (between the yoke and tube).

Yoke aligned using a test grid

Looking good!

Finishing touches:
Now, the back of the TV case can be screwed back on. The operation is almost complete and we're (finally) ready to have some fun!

Testing:

To make sure all the controls are working properly and that there are no other issues, what better way to test than to spark up some games?!

Thanks Calamity. You know, I thought that I had this SCART thing licked before trying GroovyMAME! Only once I tried running all those native video modes did the true requirements of a "SCART television as arcade monitor" reveal themselves. ;)

The reason for using the Blaupunkt case instead of the Loewe is pretty simple: the Blaupunkt chassis drives 4 ohm speakers and the Loewe has 8 ohms speakers. The shape is different so they can't easily be exchanged.

In some ways the Loewe case would be better. It's extremely sturdy and can be more easily rotated for vertical games due to it's box-like design. The CT 1170 will happily sit on its side whereas the Blaupunkt needs to be lent against something for it to stay upright.

when your at the stage of fitting the new tube to the blaupunkt chassis and youve got the yoke on the neck of the tube (powered) for final adjustment, how well does the yoke sit on the neck, do you need to shut the clamp slightly to keep in place or does it sit fairly well by itself?

Yeah, I tighten the clamp slightly so that the yoke only moves once you apply pressure. You just have to find the right balance between having it loose enough to rotate but not so loose that it just slips out of position. It's actually quite simple in practice. I guess the trick is to make the adjustments without electrocuting yourself! Obviously I haven't done that to myself yet but I'm extremely wary during that part of the operation.

It's very gratifying to see the image line up. Many of the TVs that I tested in the early days had a slight rotation to the image and I just assumed that it couldn't be fixed.

Hindsight is pretty painful in this hobby... a lot of cool units bit the dust because I didn't know how to sort out some of these simple issues!

Dear Paradroid, please don't take this as an insult, it's just that I don't understand.. All of the game screenshots are stretched to full screen. Caveman Ninja, for example, runs at a resolution of 256x240, and should therefore look more or less square, yet the screenshot fills up the whole of the screen. Why is that? Is that GroovyMame's doing or do you adjust the TV's trimpot each time you start up a game? In either case, the image gets distorted and does not look like the original.It surprises me that you nor any of those who commented object to that, as I presume all of you are authenticity hunters. Again, to all of you, be not offended. I'm just starting out in this PC2CRT thing and in a most newbish way am wondering about and struggling with modelines and aspect ratios.

Firstly, no offence caused! This is an interesting topic that you have brought up...

Classic CRTs have an aspect ratio of 4:3. They are not square. Squares have sides of equal length i.e. 1:1 ratio. Arcade screens weren't actually square.

Now, to fill to fill a 4:3 screen with pixels that are square, you need a resolution that has a 4:3 ratio e.g. 320 × 240. Same games have this. Other resolutions (such as 256 × 240) have different pixel aspects and maybe be closer to square (as with Caveman Ninja) rather than 4:3. However, most people agree that the original manufacturer's intention was to fill the screen (which is 4:3) rather than have a game with square pixels and black horizontal or vertical borders.

Perhaps the most famous example is Street Fighter II. The game runs at 384 × 224 and looks very squashed if you maintain square pixels. I don't think anyone would argue that the game wasn't designed to be sized to fill a 4:3 screen. If you don't do that, the game will look like it's letter-boxed. All the characters will look short and squashed. The SNES version looked SO much better in the '90s when I stretched it out using the vertical size control on my Commodore 1084. It always looked squashed on every other TV.

So, my personal take on this subject is that you resize the game to fill the screen to the edges. I create a small amount of overscan at the edges (so that the vertical borders are clean) and slightly underscan the top and bottom (so that you see every scanline).

I can't think of a single case where this doesn't produce the best looking result to my eyes. Even MAME stretches games to 4:3 when running at non-native resolutions so I believe my approach is the correct one.

BTW, do you really think Caveman Ninja looks distorted? I reckon it looks pretty damn good in those screenshots above!

as paradroid said it is true that it doesnt matter the 'original' resolution of the game, eg. kungfumaster at 256x256, there is no way the game designers intended that game to be run 'square' with large black borders on the sides. they expected the monitor controls to be adjusted so the game fits 4:3. generally if you prefer the look of a game which is not adjusted to fit 4:3 because you remember it differently when you were younger, it just means that when you originally played it, the screen was not set up correctly.